Over time and through repeated use, joints can become damaged or worn. For example, repetitive stress and strain on joints (e.g., strenuous activity, traumatic events, and certain diseases such as infection and rheumatoid arthritis) can cause the surfaces of the joint to wear out or otherwise break down. Such degeneration of the joint surfaces can result in pain, swelling, stiffness, deformity, and decreased mobility.
Arthroplasty procedures can be performed to repair damaged joints. During an arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned, or a prosthesis can be implanted into the damaged region. Arthroplasty procedures may take place in any of a number of different joints in the body, such as a knee, a hip, a shoulder, or an elbow.
One type of arthroplasty procedure is a total knee arthroplasty (“TKA”), in which the articulating surfaces of a knee joint are replaced or resurfaced with prosthetic implants. The knee joint may have, for example, been worn out due to degenerative arthritis, been injured from trauma or infection, or been deteriorated due to another joint disease. During a TKA procedure, the articulating surfaces of the distal femur may be resurfaced or removed and replaced with a femoral component, and the articulating surfaces of the proximal tibia may be resurfaced or removed and replaced with a tibial component. The surfaces of the femoral and tibial components are configured to articulate with each other. In some TKA procedures, the articular surface of the patella may be replaced with a patellar component, depending on the condition of the patella.
The prosthetic implants are firmly attached to the adjacent bones and have smooth articulating surfaces to allow pain-free motion. Prior to implantation of an implant, the damaged region is prepared to receive the implant. For example, in a knee arthroplasty procedure, the distal femur and/or proximal tibia, may be prepared (e.g., cut, drilled, reamed) to provide one or more surfaces that can mate with the implant and thereby physically support the implant.
Generally, when preparing the femur for arthroplasty, up to five cuts may be made on the femur, including a distal cut, an anterior cut, a posterior cut, an anterior chamfer cut and a posterior chamfer cut. Usually, a first device is used to make the distal cut. A second device, often called a 4-in-1 cutting block, is used to make the remaining four cuts. The accuracy of these cuts, including the position and orientation thereof, is an important factor in the accuracy of the alignment of implants that are fixed to the bone. A one- to two-millimeter translational misalignment, or a one- to two-degree angular or rotational misalignment, may adversely affect the outcome of the TKA procedure. For example, implant misalignment may result in intolerable post-surgery pain, and also may prevent the patient from having full knee extension and/or full and stable knee flexion.